I'm making reactive stepping stones for my backyard and I was wondering how to use an accelerometer to detect foot steps on the stone. The SnakeStomp game that SparkFun has in it's tutorials (http://www.sparkfun.com/tutorials/196) uses an accelerometer to do this, but they don't have the arduino code listed. (the code link only has the processing code the game graphics)

I've never worked with accelerometers before and would like some guidance on which one I should get. How sensitive does the sensor need to be? Would the step have to be hard or would a soft footstep also be picked up? Would this cheap sensor be sensitive enough? http://www.pololu.com/catalog/product/1246 (I believe is similar to the one used in the SnakeStomp game)

Accelerometers have a range: if you are sensing minuscule changes in acceleration due to vibrations from the highway next to your house, you want a small range, i.e. +/- 1g. But for earthquakes you may want +/-20g. You'll have to find a compromise. A small sensitivity sensor should be good, though.

You might want to try a digital accelerometer that has a built in Tap detection algorithm. You can try to tweak the settings of the algorithm to distinguish the step and generate an interrupt to the arduino.

The Pololu accelerometer would likely work under the right conditions- a stomp ought to produce a sharp, short duration acceleration. What would concern me is that if these are stones in dirt, the motion might be pretty damped, so your signal might be small. I'm guessing, though. It might be fine.

I was interested in similar signals for a different reason, and I used piezoelectric coax- it looks like thin coaxial cable, but the insulating part inside is PVDF. Stepping on this yields a big voltage, tiny current. You can get it from a company called measurement specialties, but it isn't all that convenient to buy it from them. You can find the cable on eBay, where it is sold as inexpensive pickups for amplifying guitars.

There is a nice document on how this is used in an application closer to what you are doing, with some circuit diagrams.http://www.docstoc.com/docs/8894270/PIEZO-CABLE

You can surely senses steps on rocks by using accelerometer mechanically fixed to the rocks.. however, I'd think that something like a force sensor would be better? http://www.sparkfun.com/products/9376

@jgillick: how did you finally do it? did you used an accelerometer or force sensitive resistor?

I think using an accelerometer only to detect taps/ force would be too much for cost and coding. But if you plan to use the sensor on your wrist or somewhere on your body, an accelerometer and a sensing algorithm would be better.